Anatomical motion hinged prosthesis

ABSTRACT

A hinged knee prosthesis comprises a tibial component and a femoral component. The tibial component is configured to attach to a tibia. The tibial component has a bearing surface. The femoral component is configured to hingedly attach to the tibial component and rotate relative to the tibial component. The femoral component comprises a medial condyle and a lateral condyle. The medial and lateral condyles have an eccentric sagittal curvature surface configured to rotate and translate on the bearing surface of the tibial component. A method of rotating a hinged knee through a range of flexion is provided. The method fixedly attaches a femoral component to a tibial component. Axial rotation of the femoral component is induced relative to the tibial component when the hinged knee is flexed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of pending U.S. patent applicationSer. No. 16/684,801, filed Nov. 15, 2019, which is a division of U.S.patent application Ser. No. 15/676,024, filed Aug. 14, 2017, now U.S.Pat. No. 10,779,949, issued Sep. 22, 2020, which is a continuation ofU.S. patent application Ser. No. 13/964,306, filed Aug. 12, 2013, nowU.S. Pat. No. 9,730,799, issued Aug. 15, 2017, which is a continuationof U.S. patent application Ser. No. 12/307,102, filed Feb. 3, 2010, nowU.S. Pat. No. 8,523,950, issued Sep. 3, 2013, which is a U.S. NationalPhase of International Application No. PCT/US2007/072611, filed Jun. 30,2007, which claims the benefit of U.S. Provisional Application No.60/806,383, filed Jun. 30, 2006. Each of the prior applications isincorporated by reference herein in its entirety.

BACKGROUND 1. Field

This application relates generally to knee prostheses and, moreparticularly, the application relates to hinged knee prostheses.

2. Related Art

Most hinged-knee prostheses only provide a mechanical means to restorethe joint in a hinge-like function. Other hinged-knee prostheses providefor more kinematically-correct prostheses; however, they rely mostly onremaining soft tissue to restore normal kinematics to the joint. In mostcases, the remaining soft tissue has been compromised and/ormissing/removed during surgery. Thus, the soft tissue cannot contributesignificantly to restoring normal kinematics, particularlyanterior/posterior (A/P) translation or normal axial rotation includingrotation to the ‘screw-home’ position. Moreover, the remaining softtissue may be damaged when restoring normal kinematics by forcing motionof the prostheses.

In prosthetic systems that address axial rotation, current systemsaddress rotation by allowing a rotating platform. Generally, one of thetwo articulating prostheses (usually the tibial insert or construct) isallowed rotational freedom. This allows the soft tissues to rotate thejoint in a more normal fashion. However, most soft tissue has beencompromised and cannot reproduce normal or near normal rotation.

A/P translation is a motion that is seldom addressed. In thoseprostheses that do address A/P translation, a cam mechanism against thejoint-linking mechanism (usually a post) or against the tibial articulargeometry is used to force the tibia anteriorly relative to the distalfemur as the knee flexes. This method of A/P translation is common in aprimary total knee arthroplasty (TKA) by the use of a cam and postmethod in which the cam is on the femoral articulating prosthesis andthe post is found on the tibial articulating prosthesis. This iscommonly referred to as a posterior or cruciate stabilized knee implant.These hinged knees generally focus forces on a small area (such as a camwith point and/or line contact and post), which may increase wear anddecrease the life span of the implant.

In U.S. Pat. Nos. 5,358,527 and 5,800,552, A/P translation is allowedthrough flexion, yet the hinged knee does not control and/or maintain aconstant limit on A/P translation. In other words, the femoral can beflexed and can translate posteriorly when contact to the tibial bearingsurface is not maintained. Thus, the femoral component does not maintaincontact with the tibial component when A/P translation occurs.

There remains a need in the art for kinematically-correct prosthesesincluding A/P translation and/or normal axial rotation. In addition,there remains a need for kinematically-correct prostheses that reducewear on the prosthesis and reduce forces on the remaining soft tissue.

SUMMARY

The disclosure provides a hinged knee prosthesis comprising a tibialcomponent and a femoral component. The tibial component is configured toattach to a tibia. The tibial component has a bearing surface. Thefemoral component is configured to hingedly attach to the tibialcomponent and rotate relative to the tibial component. The femoralcomponent comprises a medial condyle and a lateral condyle. The medialand lateral condyles have a sagittal curvature surface configured toinduce axial rotation on the bearing surface of the tibial component.

The medial and lateral condyles may have a plurality of eccentricsagittal curvature surfaces configured to rotate on the bearing surfaceof the tibial component.

The bearing surface of the tibial component is configured with ananterior portion and a posterior portion. The posterior portion of thebearing surface has a portion configured to guide the medial and lateralcondyles of the femoral component. Contact points between the femoralcomponent and the tibial component translate in the anterior/posteriordirection and rotate axially.

The hinged knee may further comprise an axle hinge pin. The axle hingepin is located transversely between the medial and lateral condyles. Theeccentric sagittal curvature surface has a center of rotation notaligned with the axle hinge pin.

The hinged knee prosthesis may further comprise a post configured toextend from the tibial component to the femoral component. A proximalportion of the post is configured to attach to the axle hinge pin.

The center of rotation of a portion of the eccentric sagittal curvaturesurface of the medial condyle may not be aligned with the center ofrotation of a portion of the eccentric sagittal curvature surface of thelateral condyle. The medial and lateral condyles direct axial rotationof the femoral component relative to the tibial component.

The center of rotation of a portion of the eccentric sagittal curvaturesurface of the medial condyle may be aligned with the center of rotationof a portion of the eccentric sagittal curvature surface of the lateralcondyle, wherein the medial and lateral condyles directanterior/posterior translation of the femoral component relative to thetibial component.

The medial condyle of the femoral component may further comprise aconcentric sagittal curvature surface. The center of rotation of theconcentric sagittal curvature surface of the medial condyle is notaligned with the center of rotation of a portion of the eccentricsagittal curvature surface of the lateral condyle. The medial andlateral condyles direct axial rotation of the femoral component relativeto the tibial component.

The center of rotation of a first eccentric sagittal curvature surfaceof the medial condyle may not be aligned with the center of rotation ofa first eccentric sagittal curvature surface of the lateral condyle. Themedial and lateral condyles direct axial rotation and anterior/posteriortranslation of the femoral component relative to the tibial componentwhen the first eccentric sagittal curvature surfaces contact the tibialcomponent. The center of rotation of a second eccentric sagittalcurvature surface of the medial condyle is aligned with the center ofrotation of a second eccentric sagittal curvature surface of the lateralcondyle, wherein the medial and lateral condyles directanterior/posterior translation of the femoral component relative to thetibial component when the second eccentric sagittal curvature surfacescontact the tibial component.

The hinged knee prosthesis may comprise a sleeve configured to receivethe post. The sleeve is configured to allow axial rotation of thefemoral component relative to the tibial component.

The disclosure provides a method of rotating a hinged knee through arange of flexion. The method fixedly attaches a femoral component to atibial component. Axial rotation of the femoral component is inducedrelative to the tibial component when the hinged knee is flexed.

The method may further comprise the step of inducing translation of thefemoral component in an anterior/posterior direction relative to thetibial component when the hinged knee is flexed.

The inducing translation step and the inducing axial rotation steps mayoccur simultaneously.

The inducing axial rotation step may occur through a portion of therange of flexion of the prosthetic knee.

The inducing axial rotation step may occur through a first portion ofthe range of flexion of the prosthetic knee and a second portion of therange of flexion of the prosthetic knee.

The first portion of the range of flexion may not be adjacent to thesecond portion of the range of flexion.

The inducing axial rotation step may occur at varying angular velocitiesas the hinged knee passes through the range of flexion of the knee.

The fixedly attaching step may include connecting a sleeved post to thetibial insert such that a sleeved portion of the sleeved post and a postportion of the sleeved post axially rotate relative to each other.Further the fixedly attaching step may include fixing an axial hinge pinto the sleeved post such that the axial hinge pin transversely connectsa medial condyle of the femoral component to the lateral condyle of thefemoral component.

The method may further comprise the step of fixing the sleeved portionof the sleeved post to a stem in the tibial component.

The method may further comprise the step of axially displacing thesleeved portion of the sleeved post relative to the post portion of thesleeved post when the hinged knee is flexed.

Thus, kinematically-correct prostheses including A/P translation and/ornormal axial rotation may be achieved by the structures in thedisclosure. These kinematically-correct prostheses may reduce wear onthe prosthesis and reduce forces on the remaining soft tissue. Furtherfeatures, aspects, and advantages of the present invention, as well asthe structure and operation of various embodiments of the presentinvention, are described in detail below with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate embodiments and together with thedescription, serve to explain the principles of the invention. In thedrawings:

FIG. 1 is an isometric view of an embodiment of a hinged knee;

FIG. 2 is a cutaway view of the embodiment of FIG. 1;

FIG. 3 is a side view of the embodiment of FIG. 1;

FIG. 4 is a cutaway view of the embodiment of FIG. 3;

FIG. 5 is an isometric view of an embodiment of a hinged knee;

FIG. 6 is a cutaway view of the embodiment of FIG. 5;

FIG. 7 is a side view of the embodiment of FIG. 5;

FIG. 8 is a cutaway view of the embodiment of FIG. 7;

FIG. 9 is an isometric view of an embodiment of a tibial insert;

FIG. 10 is a top view of the tibial insert of FIG. 9;

FIG. 11 is a side view of an embodiment of femoral component of a hingedknee;

FIGS. 12 and 13 are a side view and an isometric view, respectively, ofan embodiment of a hinged knee at extension;

FIGS. 14 and 15 are a side view and an isometric view, respectively, ofthe hinged knee of FIG. 12 at 20 degrees flexion;

FIGS. 16 and 17 are a side view and an isometric view, respectively, ofthe hinged knee of FIG. 12 at 40 degrees flexion;

FIGS. 18 and 19 are a side view and an isometric view, respectively, ofthe hinged knee of FIG. 12 at 90 degrees flexion;

FIGS. 20 and 21 are a side view and an isometric view, respectively, ofthe hinged knee of FIG. 12 at 120 degrees flexion;

FIGS. 22 and 23 are a side view and an isometric view, respectively, ofthe hinged knee of FIG. 12 at 150 degrees flexion;

FIGS. 24-26 are a side view, an isometric view, and a top view,respectively, of an embodiment of a hinged knee at extension;

FIGS. 27-29 are a side view, an isometric view, and a top view,respectively, of the hinged knee of FIG. 27 at 20 degrees flexion;

FIGS. 30-32 are a side view, an isometric view, and a top view,respectively, of the hinged knee of FIG. 27 at 40 degrees flexion;

FIGS. 33-35 are a side view, an isometric view, and a top view,respectively, of the hinged knee of FIG. 27 at 90 degrees flexion;

FIGS. 36-38 are a side view, an isometric view, and a top view,respectively, of the hinged knee of FIG. 27 at 120 degrees flexion; and

FIGS. 39-41 are a side view, an isometric view, and a top view,respectively, of the hinged knee of FIG. 27 at 150 degrees flexion.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring to the accompanying drawings in which like reference numbersindicate like elements, FIGS. 1-4 show views of an embodiment of ahinged knee.

Turning now to FIG. 1, FIG. 1 is an isometric view of an embodiment of ahinged knee 10. The hinged knee 10 includes a femoral component 14, atibial component 16, a pin sleeve 18 and a pin 20. The tibial component16 includes a tibial insert 24 and a tibial base 26. The femoralcomponent 14 includes a medial condyle 30 and a lateral condyle 32. Thepin 20 connects the condyles 30 and 32 to the sleeve 18. The sleeve 18connects to the tibial component through a sleeved post (discussedbelow).

As the knee flexes, the femoral component 14 rotates relative to thetibial component 16. The femoral component 14 rotates about the pin 20.Axial rotation and anterior/posterior (A/P) translation of the femoralcomponent 14 is urged by the shape of the tibial insert 24 and thecondyles 30 and 32. The axial rotation and anterior/posterior (A/P)translation of the femoral component 14 may occur because the pin 20 isable to axial rotate and be axially translated relative to the post andsleeve of the hinged knee 10.

The femoral component 14 and the tibial component 16 are connected tothe femur and tibia, respectively. Stems 36 are inserted into the femurand tibia to fix the femoral component and tibial component to thebones. The length and thickness of these stems may be adjusted basedupon required fixation, size of the bones, and size of theintramedullary canals in the bones.

Turning now to FIG. 2, FIG. 2 is a cutaway view of the embodiment ofFIG. 1. The cutaway is taken in a sagittal plane between the femoralcondyles. FIG. 2 shows the pin 20 in the sleeve 18. The sleeve 18 isattached to a post sleeve 40 which surrounds a post 42. The post 42 isattached to the tibial base 26, and may be attached asymmetrically tothe tibial base 26. The post sleeve 40 may be axially rotated andaxially translated relative to the post 42. The sleeve 18 (and thus thepin 20) may rotate axially and translate axially relative to the tibialcomponent 16. The rotation and translation allow for the femoralcomponent 14 to axially rotate and to translate in the A/P direction.The A/P translation may be accomplished by the condyle surface having acurvature with a center of rotation outside the pin 20. As the femoralcomponent 14 rotates, a bushing 46 stops hyper extension so that theknee may not overextend.

Turning now to FIG. 3, FIG. 3 is a side view of the embodiment ofFIG. 1. The pin 20 is located posterior to the center of the knee 10.The curve 50 of the condyle 32 is eccentric with respect to the centerof rotation of the femoral component 14, which is the pin 20. Withrespect to the tibial component 16, the pin 20 axially rotates andaxially translates as the knee flexes.

Turning now to FIG. 4, FIG. 4 is a cutaway view of the embodiment ofFIG. 3. The cutaway is taken along the same sagittal plane of thecutaway in FIG. 2. The cutaway shows the post sleeve 40 and post 42 ofthe hinged knee 10. A screw 56 fixes a post receiver 58 to the post tolock the post sleeve 40 on the post 42. The post sleeve 40 and pinsleeve 18 then may rotate and translate axially without pulling off thepost 42.

Turning now to FIGS. 5-8, these FIGs. show views of another embodimentof a hinged knee 70. Turning now to FIG. 5, FIG. 5 is an isometric viewof an embodiment of the hinged knee 70. The hinged knee 70 includes afemoral component 74, a tibial component 76, a pin sleeve 78 and a pin80. The tibial component 76 includes a tibial insert 84 and a tibialbase 86. The femoral component 74 includes a medial condyle 90 and alateral condyle 92. The pin 80 connects the condyles 90 and 92 to thesleeve 78. The sleeve 78 connects to the tibial component through asleeved post.

As the knee flexes, the femoral component 74 rotates relative to thetibial component 76. The femoral component 74 rotates about the pin 80.Axial rotation and anterior/posterior (A/P) translation of the femoralcomponent 74 is urged by the shape of the tibial insert 84 and thecondyles 90 and 92. The axial rotation and anterior/posterior (A/P)translation of the femoral component 74 may occur because the pin 80 isable to axially rotate and be axially translated relative to the postand sleeve of the hinged knee 70.

The femoral component 74 and the tibial component 76 are connected tothe femur and tibia, respectively. Stems 96 are inserted into the femurand tibia to fix the femoral component and tibial component to thebones. The length and thickness of these stems may be adjusted basedupon required fixation, size of the bones, and size of theintramedullary canals in the bones.

Turning now to FIG. 6, FIG. 6 is a cutaway view of the embodiment ofFIG. 5. The cutaway is taken in a sagittal plane between the femoralcondyles. FIG. 6 shows the pin 80 in the sleeve 78. The sleeve 78 isattached to a post 100 which is inserted into a post sleeve 102. Thepost sleeve 102 is attached to the tibial base 86. The post 100 may beaxially rotated and axially translated relative to the post sleeve 102.The pin sleeve 78 (and thus the pin 80) may rotate axially and translateaxially relative to the tibial component 76. The rotation andtranslation allow for the femoral component 74 to axially rotate and totranslate in the A/P direction. The A/P translation may be accomplishedby the condyle surface having a curvature with a center of rotationoutside the pin 80. As the femoral component 74 rotates, a bushing 106stops hyper extension so that the knee may not overextend.

Turning now to FIG. 7, FIG. 7 is a side view of the embodiment of FIG.5. The pin 80 is located posterior to the center of the knee 70. Thecurve 110 of the condyle 92 is eccentric with respect to the center ofrotation of the femoral component 74, which is the pin 80. With respectto the tibial component 76, the pin 80 axially rotates and axiallytranslates as the knee flexes.

Turning now to FIG. 8, FIG. 8 is a cutaway view of the embodiment ofFIG. 7. The cutaway is taken along the same sagittal plane of thecutaway in FIG. 6. The cutaway shows the post 100 and post sleeve 102 ofthe hinged knee 70. An enlarged portion 106 of the post 100 fixes thepost 100 to the femoral component 74 so that when the post 100 isinserted in the post sleeve 102, the femoral component 74 is aligned andheld in place relative to the tibial component 76. The post 100 and pinsleeve 78 then may rotate and translate axially without pulling thefemoral component 74 off the tibial base 76.

Turning now to FIGS. 9 and 10, these FIGs. show views of a tibial insert120. FIG. 9 is an isometric view of an embodiment of a tibial insert 120and FIG. 10 is a top view of the tibial insert 120 of FIG. 9. The tibialinsert 120 includes a post hole 124 for receiving the post from eitherthe tibial base or the femoral component. Direction lines 126 on abearing surface 128 show the lines the femoral component articulates onthe tibial insert 120. As the femoral component rotates on the insert120, the position on the line 126 travels posteriorly. The posteriorportion of the tibial insert 120 slopes to axially rotate and translatethe femoral component posteriorly. Together in conjunction with thecurvature of the condyles, the tibial insert 120 cause A/P translationand axial rotation of the femoral component.

Turning now to FIG. 11, FIG. 11 is a side view of an embodiment offemoral component 130 of a hinged knee. The curvature of a condyle 131includes a first distal portion 132 having a first center of rotation134, a second posterior portion 136 having a second center of rotation138 concentric with a pin hole 140, and a third proximal portion 142having a third center of rotation 144. The centers of rotation 134 and144 are eccentric to the pin hole 140. As the knee rotates, the contactpoint between the femoral component 130 and the tibial insert produces aforce normal to the femoral component 130 and aligned with the center ofrotation for that section of the curvature. While the contact point iswithin the distal portion of the curvature, the normal force pointstoward the center of rotation 134. At the interface between the distalportion 132 and the posterior portion 136, the normal force is collinearwith the centers of rotation 134 and 138. Similarly, at the interfacebetween the posterior portion 136 and the proximal portion 142, thenormal force is collinear with the centers of rotation 138 and 144.Thus, the contact points do not jump during rotation but smoothly move.

The eccentricity of the curvatures allows for the lateral forces at thecontact points to control axial rotation and A/P translation. Becausethe forces are normal to the tibial and femoral surfaces, reactiveforces at the contact points induce A/P motion and axial rotation. Thepins, sleeves, and posts of the hinged knee allow for the translationand rotation of the femoral component 130 with respect to the tibialcomponent.

Turning now to FIGS. 12-23, the FIGs. show side views and isometricviews of an embodiment of a hinged knee in different angles of flexion.FIGS. 12 and 13 are a side view and an isometric view, respectively, ofan embodiment of a hinged knee at extension. A contact point 150anterior to the pin axis is the contact point between a femoralcomponent 152 and a tibial component 154. The tibial component isposteriorly distal sloped at the contact point 150 so there is areactive contact force attempting to push the femoral componentbackwards. FIG. 13 shows the position of the femoral component 152 atextension.

Turning now to FIGS. 14 and 15, FIGS. 14 and 15 are a side view and anisometric view, respectively, of the hinged knee of FIG. 12 at 20degrees flexion. As the knee flexes, the contact point 150 movesposteriorly. Additionally, as shown in FIG. 15, the femoral component152 has rotated relative to the tibial component 154. The axial rotationis urged by a differential between the moments created by the reactiveforces at the medial and lateral condyles.

Turning now to FIGS. 16 and 17, FIGS. 16 and 17 are a side view and anisometric view, respectively, of the hinged knee of FIG. 12 at 40degrees flexion. The contact point 150 has shifted posteriorly and thefemoral component has continued to rotate axially. This change incontact point shows the A/P translation of the femoral component as theknee rotates. While most of the motion during early knee flexion isaxial rotation, some A/P translation occurs. This “rollback” androtation is similar to normal joint kinematics. These movements areurged by the shapes of the tibial and femoral component. This minimizesshear forces on the patella which may otherwise try to force thesemovements of the femoral components. Generation of the shear forces inthe patella may cause pain or prosthetic failure.

The contact force 150 is directed through the center of the pin hole asthe curvature of the condyle transitions from the distal eccentricportion to the posterior concentric portion discussed with reference toFIG. 11.

Turning now to FIGS. 18 and 19, FIGS. 18 and 19 are a side view and anisometric view, respectively, of the hinged knee of FIG. 12 at 90degrees flexion. While flexion continues through the concentric portion,the A/P translation and axial rotation stops. The distance to the centerof the pin hole remains constant as the center of curvature for theposterior portion of the condyle is concentric with the pin hole.

Turning now to FIGS. 20 and 21, FIGS. 20 and 21 are a side view and anisometric view, respectively, of the hinged knee of FIG. 12 at 120degrees flexion. The contact force 150 is directed through the center ofthe pin hole as the curvature of the condyle transitions from theposterior concentric portion of the curvature to the proximal eccentricportion discussed with reference to FIG. 11. As the contact force 150moves posterior the center of the pin hole, the distance from thecontact point to the center of the pinhole lessens.

Turning now to FIGS. 22 and 23, FIGS. 22 and 23 are a side view and anisometric view, respectively, of the hinged knee of FIG. 12 at 150degrees flexion. As the hinged knee continues to rotate, the contactforce generally creates A/P translation, and little axial rotation.Again, this is generally consistent with normal knee kinematics. Whilethis embodiment has described A/P translation and axial rotation bysurface characteristics of the tibial and femoral components 154 and152, other embodiments may accomplish these motions in other ways.

The additional embodiments generally try to control lateral forcesbetween the femoral and tibial components. For example, differences inthe lateral forces between condyles may create motion. Additionallykeeping lateral forces on one side small or zero while controlling theforces on the other side can control axial rotation. For more rotation,forces may be opposite in direction to increase axial rotation. Becauserotation is controlled by moments, another method of controllingrotation is to control the moment arms.

Another embodiment may create contact points with corresponding tibialarticulation of the femoral articulating surfaces to vary from a planeperpendicular to the transverse axle hinge pin. Generally, the planewould extend through a medial/lateral and/or lateral/medial direction.As the knee moves through the range of motion of the knee, thecorresponding insert articulating geometry remains parallel or variesfrom the same plane creating an axial rotation through whole, in part,and/or various ranges of the range of motion of the joint.

In another embodiment, a concentric sagittal curvature of the medial orlateral femoral condyle's articular surface relative to the transversehinge pin location and the opposite femoral condyle's articular surfacemay have eccentric curvature sagittally to the hinge pin location. Thisshifts the contact with the tibial articulation medial/lateral orlateral/medial at least in part through a range of motion. The tibialarticulating surfaces correspond to femoral curvatures and induce axialrotation through whole, in part, and/or various ranges of the range ofmotion of the joint.

Alternatively, a concentric sagittal curvature of the medial or lateralcondyle's articular surface relative to the transverse hinge pinlocation and the opposite condyle's articular surface having eccentriccurvature sagittally to the hinge pin location may create the motion.The tibial articulating surfaces corresponds to femoral curvatures wherethe corresponding eccentric medial or lateral compartment follows apredetermined path relative to multiple angles of flexion and itscorresponding contact points movement. The radial translation of thesecontact points around the axial rotation around the tibial post/sleeveaxis and the corresponding concentric medial or lateral compartmentfollows a predetermined path relative to multiple angles of flexion andits corresponding contact point's movement around the axial rotationaround the tibial post/sleeve axis. This induces an axial rotationthrough whole, in part, and/or various ranges of the range of motion ofthe joint.

Another embodiment includes a femoral prosthesis with eccentric sagittalcurvature for both of the medial and lateral articulating condylarportions of the femoral prosthesis relative to the transverse axle pinposition. A tibial insert with the corresponding articulating geometry,either inclining and/or declining as the eccentric contact points of thefemoral articulation translates, shift in a medial/lateral and/orlateral/medial direction to induce an axial rotation through whole, inpart, and/or various ranges of the range of motion of the joint.

In another embodiment, a concentric sagittal curvature of the medial orlateral condyle's articular surface relative to the transverse hinge pinlocation and the opposite condyle's articular surface having eccentriccurvature sagittally to the hinge pin location. The tibial articulatingsurfaces correspond to femoral curvatures where the correspondingeccentric medial or lateral compartment follows a predetermined pathrelative to multiple angles of flexion and its corresponding contactpoints movement and the radial translation of these contact pointsaround the axial rotation around the tibial post/sleeve axis. Thecorresponding concentric medial or lateral compartment follows apredetermined inclining and/or declining path relative to multipleangles of flexion and its corresponding contact points movement aroundthe axial rotation around the tibial post/sleeve axis which induces anaxial rotation through whole, in part, and/or various ranges of therange of motion of the joint.

Alternatively, a femoral prosthesis with concentric sagittal curvaturefor both of the medial and lateral articulating condylar portions of thefemoral prosthesis relative to the transverse pin position. A tibialinsert with the corresponding articulating geometry, either incliningand/or declining, form an axial rotating path relative to the femoralarticulating surfaces. Translational/rotational freedom allows thetransverse pin to rotate and translate the femoral prosthesis.

Turning now to FIGS. 24-41, the FIGs. Show side views, isometric views,and top views of an embodiment of a hinged knee in different angles offlexion. FIGS. 24-26 are a side view, an isometric view, and a top view,respectively, of an embodiment of a hinged knee at extension. A femoralcomponent 180 rotates about a pin 182 relative to a tibial component184. Contact areas 200 show the area in which a tibial insert 186 maycontact the femoral component 180. The contact areas 200 in FIGS. 24-41show how the femoral component 180 rotates and translates along thetibial insert 186.

Turning now to FIGS. 27-29, FIGS. 27-29 are a side view, an isometricview, and a top view, respectively, of the hinged knee of FIG. 27 at 20degrees flexion. The femoral component 180 continues to rotate about thepin 182 relative to the tibial component 184. The contact areas 200,particularly the lateral contact area, have rolled back. The roll backof the lateral contact area corresponds to axial rotation of the femoralcomponent 180 relative to the tibial component 184.

Turning now to FIGS. 30-32, FIGS. 30-32 are a side view, an isometricview, and a top view, respectively, of the hinged knee of FIG. 27 at 40degrees flexion. The femoral component 180 continues to rotate about thepin 182 relative to the tibial component 184. The contact areas 200 havecontinued to roll back, and again the lateral contact area hastranslated farther posteriorly compared to the medial condyle. Thiscorresponds to more axial rotation.

Turning now to FIGS. 33-35, FIGS. 33-35 are a side view, an isometricview, and a top view, respectively, of the hinged knee of FIG. 27 at 90degrees flexion. The femoral component 180 continues to rotate about thepin 182 relative to the tibial component 184. From 40 degrees to 90degrees of flexion, the rotation and translation are minimized as therotation continues through the concentric portion of the curvature.

Turning now to FIGS. 36-38, FIGS. 36-38 are a side view, an isometricview, and a top view, respectively, of the hinged knee of FIG. 27 at 120degrees flexion. The femoral component 180 continues to rotate about thepin 182 relative to the tibial component 184. Similar to the flexionbetween 40 and 90 degrees, from 90 degrees to 120 degrees of flexion,the rotation and translation are minimized as the rotation continuesthrough the concentric portion of the curvature.

Turning now to FIGS. 39-41, FIGS. 39-41 are a side view, an isometricview, and a top view, respectively, of the hinged knee of FIG. 27 at 150degrees flexion. The femoral component 180 continues to rotate about thepin 182 relative to the tibial component 184. As the flexion continuesfrom 120 to 150 degrees, the contact areas 200 translate and have littleaxial rotation.

Thus, as the knee flexes, the rotation allows for the patella to slidealong the patellar groove without generating forces in the patella.Additionally, with movement approximating the natural movement, thehinged knee does not generate forces in the soft tissue. This may helppreserve soft tissue that is initially damaged by surgery. Moreover,some soft tissue is removed during surgery, and thus the remaining softtissue must work harder to complete tasks. Reducing the forces on softtissue can reduce swelling, pain and additional stresses on the softtissue after surgery.

In view of the foregoing, it will be seen that the several advantages ofthe invention are achieved and attained.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical application to therebyenable others skilled in the art to best utilize the invention invarious embodiments and with various modifications as are suited to theparticular use contemplated.

As various modifications could be made in the constructions and methodsherein described and illustrated without departing from the scope of theinvention, it is intended that all matter contained in the foregoingdescription or shown in the accompanying drawings shall be interpretedas illustrative rather than limiting. Thus, the breadth and scope of thepresent invention should not be limited by any of the above-describedexemplary embodiments, but should be defined only in accordance with thefollowing claims appended hereto and their equivalents.

1. A knee prosthesis comprising: a tibial component configured to attachto a patient's tibia, the tibial component including a bearing surfacewith a posterior portion, the posterior portion including medial andlateral posterior portions each having a contour that slopes medially ina posterior direction, the tibial component having a superior-inferioraxis; and a femoral component configured to attach to a patient's femur,the femoral component being hingeably coupled to the tibial component sothat the femoral component translates in an anterior/posterior (A/P)direction relative to the tibial component and axially rotates relativeto the tibial component about the superior-inferior axis, the femoralcomponent comprising: a medial condyle and a lateral condyle, whereinthe medial condyle includes a concentric sagittal curvature surface, thelateral condyle including an eccentric sagittal curvature surface, and acenter of rotation of the concentric sagittal curvature surface of themedial condyle is not aligned with the center of rotation of a portionof the eccentric sagittal curvature surface of the lateral condyle. 2.The knee prosthesis of claim 1, wherein the medial condyle and thebearing surface define defining a medial contact surface where themedial condyle contacts the bearing surface and the lateral condyle andthe bearing surface define a lateral contact surface where the lateralcondyle contacts the bearing surface; and wherein, in use, the lateralcontact surface rolls back to a greater extent than the medial contactsurface so that the lateral condyle translates to a greater extentposteriorly relative to the medial condyle.
 3. The knee prosthesis ofclaim 1, further comprising an insert positioned between the tibialcomponent and the femoral component, the insert including the bearingsurface.
 4. The knee prosthesis of claim 1, further comprising a pin,the femoral component rotates about the pin relative to the tibialcomponent.
 5. The knee prosthesis of claim 4, wherein the pin isarranged and configured to axially rotate and axially translate in theA/P direction to enable rotation and translation of the femoralcomponent relative to the tibial component.
 6. The knee prosthesis ofclaim 4, wherein the femoral component includes a pin sleeve, the pinbeing positioned within the pin sleeve for coupling the pin sleeve tothe medial and lateral condyles.
 7. The knee prosthesis of claim 6further comprising a post passing through a portion of the pin sleeveand into the tibial component.
 8. The knee prosthesis of claim 7,wherein the pin sleeve includes an opening formed therein, the postpassing through the opening for coupling the pin sleeve to the tibialcomponent.
 9. The knee prosthesis of claim 8, wherein the post extendsfrom the tibial component.
 10. The knee prosthesis of claim 8, whereinthe post is asymmetrically positioned relative to the tibial component.11. The knee prosthesis of claim 8, further comprising a post sleeve forcoupling the post to the pin sleeve, the post sleeve being positionedbetween the post and the opening formed in the pin sleeve.
 12. The kneeprosthesis of claim 11, wherein the post sleeve is arranged andconfigured to rotate and translate relative to the post.
 13. The kneeprosthesis of claim 12, wherein the pin is arranged and configured torotate and translate relative to the post and the post sleeve.
 14. Theknee prosthesis of claim 4, wherein the pin is positioned posteriorlyrelative to a center of the knee prosthesis.